From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753297AbbDPPjo (ORCPT ); Thu, 16 Apr 2015 11:39:44 -0400 Received: from www.linutronix.de ([62.245.132.108]:44509 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751875AbbDPPji convert rfc822-to-8bit (ORCPT ); Thu, 16 Apr 2015 11:39:38 -0400 Date: Thu, 16 Apr 2015 17:39:36 +0200 From: Sebastian Andrzej Siewior To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andreas Messerschmid Subject: Re: [PATCH] lockdep: make print_lock_name() robust against non-existing lock_class Message-ID: <20150416153936.GA7093@linutronix.de> References: <1429104276-22412-1-git-send-email-bigeasy@linutronix.de> <20150415141440.GQ23123@twins.programming.kicks-ass.net> <552FCC2D.4050304@linutronix.de> <20150416153503.GC12676@worktop.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20150416153503.GC12676@worktop.ger.corp.intel.com> X-Key-Id: 2A8CF5D1 X-Key-Fingerprint: 6425 4695 FFF0 AA44 66CC 19E6 7B96 E816 2A8C F5D1 User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra | 2015-04-16 17:35:03 [+0200]: >On Thu, Apr 16, 2015 at 04:50:21PM +0200, Sebastian Andrzej Siewior wrote: > >> Andreas confirmed that it works for him on v3.18 with minor adjustment. >> >> <--- >> + struct held_lock lock = READ_ONCE(*hlock); >> + unsigned int class_idx = lock.class_idx; >> ---> >> > >I'm confused by the need for that. What was the failure with the >proposed patch? It was tested on v3.18, there might have been a change between v3.18 & 4.0. The patch as-is did no compile: in file included from arch/x86/include/asm/current.h:4:0, from include/linux/mutex.h:13, from kernel/locking/lockdep.c:29: kernel/locking/lockdep.c: In function ‘print_lock’: kernel/locking/lockdep.c:558:37: error: ‘typeof’ applied to a bit-field unsigned int class_idx = READ_ONCE(hlock->class_idx); ^ include/linux/compiler.h:262:20: note: in definition of macro ‘READ_ONCE’ ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) ^ include/linux/compiler.h:262:11: error: cannot take address of bit-field ‘class_idx’ ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) ^ kernel/locking/lockdep.c:558:27: note: in expansion of macro ‘READ_ONCE’ unsigned int class_idx = READ_ONCE(hlock->class_idx); ^ include/linux/compiler.h:262:88: error: ‘sizeof’ applied to a bit-field ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) ^ kernel/locking/lockdep.c:558:27: note: in expansion of macro ‘READ_ONCE’ unsigned int class_idx = READ_ONCE(hlock->class_idx); ^ scripts/Makefile.build:258: recipe for target 'kernel/locking/lockdep.o' failed Sebastian